docs: def execute(self, callback=None):
          """
          Given the command-line arguments, this figures out which subcommand is
          being run, creates a parser appropriate to that command, and runs it.
          """
          # Preprocess options to extract --settings and --pythonpath.
          # These options could affect the commands that are available, so they
          # must be processed early.
          self.parser = parser = NewOptionParser(prog=self.prog_name,
                               usage=self.usage_info,
  #                             version=self.get_version(),
                               formatter = NewFormatter(),
                               add_help_option = False,
                               option_list=self.option_list)
          
          if not self.global_options:
              global_options, args = parser.parse_args(self.argv)
              global_options.apps_dir = os.path.normpath(os.path.join(global_options.project, 'apps'))
              handle_default_options(global_options)
              args = args[1:]
          else:
              global_options = self.global_options
              args = self.argv
  
          if global_options.envs:
              for x in global_options.envs:
                  if '=' in x:
                      k, v = x.split('=')
                      os.environ[k.strip()] = v.strip()
                  else:
                      print ('Error: environment variable definition (%s) format is not right, '
                             'shoule be -Ek=v or -Ek="a b"' % x)
  
          global_options.settings = global_options.settings or os.environ.get('SETTINGS', 'settings.ini')
          global_options.local_settings = global_options.local_settings or os.environ.get('LOCAL_SETTINGS', 'local_settings.ini')
          
          if callback:
              callback(global_options)
              
          if len(args) == 0:
              if global_options.version:
                  print self.get_version()
                  sys.exit(0)
              else:
                  self.print_help(global_options)
                  sys.ext(1)
  
          self.do_command(args, global_options)